Electric-field enhancement devices, such as sensor devices, Raman spectroscopy devices, and the like, that utilize an electric-field enhancement effect of a phenomenon of localized plasmon resonance on a metal surface are known. The Raman spectroscopy is a method for obtaining a Raman scattered light spectrum (Raman spectrum) by separating scattered light obtained by projecting single wavelength light onto a substance, and it is used for identifying a substance or the like.
The Raman spectroscopy includes a method called surface-enhanced Raman spectroscopy (SERS) that utilizes an optical field enhanced by localized plasmon resonance in order to enhance weak Raman scattered light as described, for example, in S. Ghadarghadr et al., “Plasmonic array nanoantennas on layered substrates: modeling and radiation characteristics”, Optics Express, Vol. 17, No. 21, pp. 18556-18570, 2009. This makes use of the principle that if light is projected onto a metal body, in particular, onto a metal body having a nano-order uneven pattern on a surface with a substance being in contact with the surface, optical field enhancement occurs due to localized plasmon resonance and the intensity of Raman scattered light of the sample in contact with the surface of the metal body is enhanced. The surface-enhanced Raman spectroscopy may be implemented by using a substrate having an uneven metal structure on a surface as a carrier (substrate) for carrying a subject.
As for the substrate having a fine uneven metal structure on a surface, a substrate manufactured by forming an uneven pattern on a surface of a Si substrate and forming a metal film on the surface of the uneven pattern is mainly used as described, for example, in PCT Japanese Publication No. 2006-514286, Japanese Patent No. 4347801, and Japanese Unexamined Patent Publication No. 2006-145230.
Further, a substrate produced by anodizing a surface of an Al substrate to turn a portion into a metal oxide (Al2O3) layer and filling a metal in a plurality of fine pores spontaneously formed in the metal oxide layer during the anodizing process and opens at the surface of the metal oxide layer is also proposed as described, for example, in Japanese Unexamined Patent Publication No. 2005-172569.